The present invention relates to a recording and reproducing apparatus, an information signal recording and reproducing system and a method of managing invalid area information for use with a recording and reproducing system using a so-called data recorder as a storage apparatus in which data supplied from a host computer is digitally recorded on a recording medium and data digitally recorded on the recording medium is reproduced in response to a request from the host computer.
Digital data recorders (referred to hereinafter as "data recorders") have hitherto been known to digitally record information to be recorded, i.e., file data, such as document data, program data, image data and audio data used on a computer on a magnetic tape so as to form helical tracks.
The simplest system employing the data recorder is arranged as follows. A host computer and a SCSI (small computer systems interface) formatter are connected via an SCSI interface, and the SCSI formatter and a data recorder are connected via an RS422 interface. The SCSI formatter is adapted to form a file format on a tape to exchange data on the file format.
The format used by the data recorder will bs described below. A logical volume that is equivalent to one drive on a hard disk or the like, for example, is set on the tape. One volume is composed of volume information formed of position information of various data in the logical volume and directory information composed of information provided within a directory. The directory information is read out by the SCSI formatter when a tape cassette is loaded onto the data recorder and stored in a memory of the SCSI formatter. File data or the like supplied from the host computer is recorded behind the directory information.
The host computer issues a write command. Then, when file data (or a plurality of file data) is supplied to the SCSI formatter, the SCSI formatter sequentially accumulates file data supplied thereto in a buffer. When the host computer does not issue the next write command, the SCSI formatter adds data called EOD (end of data) to the last porion of data accumulated in the buffer and transfers the data stored in the buffer to the data recorder. The data recorder records data supplied thereto from the SCSI formatter on the tape so as to form slant tracks.
The EOD is information required by the SCSI formatter to recognize the status of recorded data and to control the data recorder based on such recognition when the host computer issues the next command.
If the next command issued by the host computer is a write command, then when file data (or a plurality of file data) to be written next is stored in the butter of the SCSI formatter, the SCSI formatter adds the EOD to the last portion of the data stored in the buffer and transfers the same to the data recorder. Simultaneously, the SCSI formatter sets the tape position of the data, recorder to the position of the EOD recorded on the tape, whereby data supplied to the data recorder is sequentially recorded from the position of the EOD recorded on the tape. Accordingly, the previously-recorded EOD is erased by new data to be recorded next. Also, new EOD is added to the last portion of the new data, which as a result extends the USER area.
The SCSI formatter updates the directory information stored in the memory when data is written by the electron of write command. After the data is written, the directory information on the tape is updated by recording the directory information stored in the memory at the position where the directory information is recorded on the tape. Accordingly, when any command is supplied to the SCSI formatter from the host computer, the SCSI formatter constantly obtains accurate directory information on the tape by reading the updated directory information and can control the data recorder based on the accurate directory information.
U.S. Pat. No. 5,313,341 and Japanese laid-open patent publication No. 5-128807 describe the techniques relating to the above-mentioned recording and reproducing apparatus.
When the SCSI formatter records directory information on the tape of the tape cassette loaded onto the data recorder, if directory information cannot be updated because the supply of power to the data recorder and the SCSI formatter is stopped or because the data recorder and the SCSI formatter are failed, the tape cassette used at that time cannot be used any more.
The reason for this is that, although the directory structure on the tape is changed by the write operation, the directory information is not updated and hence information recorded on the tape cannot be accessed by the reference directory information.
When any accident occurs and the file format is troubled as described above, it in necessary to carry out a recovery operation to reconstruct a file format. In order to carry out the recovery operation, the SCSI formatter enables the data recorder to read the tape from its beginning to the end. Then, the SCSI formatter detects the directory structure oil the tape by checking all resulting data. Thereafter, directory information has to be generated one more time based on the detected result. Therefore, the processing in the recovery operation becomes complex and takes plenty of time.